Infusions of prostaglandins E1, E2, A1 and A2 produced dose-dependent rises in intraocular pressure during the 10-min and 30-min period of infusions in rabbits. Similar infusions of prostaglandin B1, prostaglandin F2a, 15-keto prostaglandin E1, 15-keto 13,14 dihydro prostaglandin E1, histamine, 5-hydroxytryptamine and bradykinin did not elevate intraocular pressure. These results raised a possibility that elevation in blood levels of PGE and PGA might be significant in the pathophysiology of ocular hypertension in glaucoma. Furthermore, antagonism of this ocular response to prostaglandin E and prostaglandin A by topical pretreatment with epinephrine and by i.m. pretreatments with progesterone steroids or glucocorticoids suggested new approaches in research in glaucoma therapy. The role of prostaglandins in human glaucoma is investigated by measuring the intraocular pressure responses during the prostaglandin i.v. infusion in human volunteers. In addition, the intraocular pressure and blood prostaglandin level are measured in control volunteers and in patients which open angle glaucoma and narrow angle glaucoma. Preliminary studies did show significantly higher prostaglandin levels in blood samples from open angle glaucoma and narrow angle glaucoma than that from nonglaucoma patients. Experiments on C14-prostaglandin E1 infusion in rabbits may add valuable information on the distribution of infused PGE1 in the intraocular tissues as well as in other organs.